Laboratory-scale analyses of matrix-conduit exchange in a karst aquifer system using coupled physical and numerical...

In karst aquifer systems, water exchange between the matrix and conduits is jointly governed by hydrodynamic conditions and the system's structural characteristics. Its complex spatiotemporal dynamics profoundly influence the recharge and discharge of the system. This study firstly developed a physical model of water exchange between the matrix and the conduit, conducted parameter calibration based on this model, and subsequently established a corresponding numerical model. Under various recharge modes, systematic analysis of the staged characteristics of water exchange was performed through both physical modeling and numerical simulation. By leveraging the parametric controllability of the numerical model, the mechanisms through which key parameters regulate water exchange were elucidated. The results indicate that different recharge modes induce dynamic variations in the hydraulic head difference between the matrix and the conduit, which directly determines the direction of water exchange, while the recharge intensity governs the magnitude of the exchange. Furthermore, parameters such as matrix hydraulic conductivity, matrix specific yield, conduit wall hydraulic conductivity, and conduit tortuosity not only influence exchange flow but also control the timing of the peak exchange flow value and the continuity of the exchange process. Further sensitivity analysis reveals significant differences in the degree of influence among different parameters, with matrix specific yield, conduit wall hydraulic conductivity, and conduit tortuosity exhibiting the most pronounced effects. These findings provide a crucial basis for evaluating karst hydraulic connectivity and dynamic responses, ultimately supporting the sustainable utilization of groundwater resources.